Production of rustless iron



Patented Mar. '29, 1938 UITED QSTTES OFFICE,

Rustless Iron and Steel Corporation, Baltimore, Md., a corporation of Delaware No Drawing. Original application September 11,

1936, ,Serial No. 100,381. Divided and this application June 5, 1937, Serial No. 146,693

1 Claim.

duction of chromium-manganese irons and steels (irons and steelsanalyzing approximately, chromium 10% to 35%, manganese 6% to carbon .05% to .15% for the alloy iron and .15% to 1% for the alloy steel, together with desired supplementary additions of nickel, copper, aluminum, silicon, molybdenum, tungsten and the like for special purposes and with the usual low percentages of sulphur and phosphorus and the balance substantially iron), and especially to, the simple, direct and thoroughly reliable production of chromium-manganese irons, employing inexpensive and readily available raw materials and utilizing known furnacing and operating equipment.

The invention accordingly consists in the combination of elements, mixture of materials and composition of ingredients and in the several steps and the relation of each of the same to one or more of the others as described herein and the scope of the application of which is indicated in the following claim.

As conducive to a clearer understanding 01. certain features of my invention it may be noted at this point that in various marine, aviation, automotive, industrial and architectural applications where a bright surface pleasing to the eye and resistant to the corrosive attack .of various acid, alkali or salt atmospheres or solutions is required, or where metal which is strong, tough and durable and resistant to the corrosive attack-of various acids, alkalies'and salts at high temperatures is required, the well known austenitlc chromium-nickel irons and steels are in widespread use at the present time. The extent of the use of such alloy irons and steels is greatly handicapped, however, 'by the comparative great expense of these materials as compared with ordinary irons and steels which are less attractive to the eye and which are less resistant to corrosive attacks of the atmosphereor various acid, alkali and salt mediums.

While numerous substitutes have been pm- I posed for the expensive austenitic chromiumnickel irons and steels the only alloy iron or steel which has gained any present-day favor is the chromium-manganese iron or steel, thegeneral analysis of which is indicated above.

In the production of chromium-manganese irons and steels, and particularly in the production of the high chromium high manganese irons and steels, which are largely austenitic in structure, in accordance with heretofore known and/or used methods of production the expensive sources of chromium and manganese, are added to a bath of low carbon iron maintained at a desired temperature. Such methods of production, while simple in procedure, require prolonged heating with a continuous consumption of power and yield a very expensive product, largely because of the great expense of the raw materials used in obtaining the alloying additions, chromium and manganese.

While known methods of producing chromiummanganese irons and steels are ordinarily satisfactory in the production of the usual low chromium low manganese alloys these methods as applied to the production of high chromium high manganese austenitic irons and steels render the product prohibitively expensive. In fact, the cost of producing the austenitic chromium-manganese irons and steels in accordance with known and/ or used methods is so great that the margin of savlugs over the production of the well-known austenitic chromium-nickel irons and steels is so small that there is little incentive to replace, for general purposes, these costly irons and steels with the chromium-manganese irons and steels.

One of the outstanding objects of my invention, therefore, is the production of high chromium high manganese irons'and steels, and especially the production of austenitic chromium-manga-. nese irons in a simple, direct and economical 40 manner employing inexpensive and readily available raw materials in the most economical proportions depending upon the availability and fluctuations in current market prices, achieving high grade, sound, clean metal which may be manufactured and sold at a price considerably beneath that of the comparatively expensive chromium-nickel irons and steels and which may be introduced into a wider range of applications supplanting known inferior, but less expensive metals. I

In the practice of my invention a material high in manganese content, such as any one of the manganese ores, pyrolusite MnOz, manganite MnO(OH), hausmannite M11304, braunite SMmOaMnSlOa, rhodocrosite M11003 and/or high carbon ferromanganese (produced by smelting any one of the above ores with coke achieving a product analyzing approximately, iron 10% to 30%, manganese 80% to 60%, silicon 1% and carbon 5% to 8%) is melted down in a suitable furnace with chrome ore FeOCrzOa and/or high carbon ferrochrome (produced by smelting this ore with coke and silica achieving a product analyzing approximately, 60% to 70% chromium,' 4% to 7% carbon, 20% to 30% iron) and a de-' sired quantity of available low carbon steel scrap, either with or without a readily available amount of high chromium high manganese iron or steel scrap or straight chromium rustless iron or steel scrap or high manganese iron or steel scrap, and a suflicient quantity of an oxidizing agent, such as roll scale or magnetic iron ore concentrate to exclude and/or remove carbon from the ingredients, thereby forming a bath of ferrous metal containing manganese and chromium with an overlying oxidizing slag rich in the oxides of chromium and manganese.

To assure the production of sound metal, free from gas-pockets, pits and the like, the large quantities of ore used are, preferably, thoroughly dried at a high temperature prior to charging into'the furnace. The pre-drying of the ores is carried out in any suitable manner, as by a long heating in a rotary gas-fired kiln at such temperatures as to rid the ores of substantially all free and combined moisture normally present. The use of predried materials effectively minimizes the amount of moisture introduced into the furnace and consequently limits the amount of hydrogen available to contaminate the metal during melt-down, as a result of the decomposition of this moisture by the action of the electric furnace arcs, and to subsequently come out during solidification of the metal after teeming to cause gas-pockets and like defects, all as more particularly indicated in the Patent No. 1,925,916 granted to William Bell Arness on September 5, 1933 and entitled Process of producing alloys.

In order to achieve temperatures sufficiently high to effectively melt the refractory ingredients comprising the charge, an electric arc furnace is preferably employed as a means of heating and furnacing the ingredients. Conveniently, a Heroult furnace, or other furnace of the direct arc type, employing carbon or graphite electrodes and lined with chromite brick to a.

height somewhat above the slag line and having side-walls and roof of silica brick is used in this practice.

Prior to charging the ingredients into the electric arc furnace, the furnace is preheated in any suitable manner, as by arcing the furnace on electrode butts or by means of a gas torch. After the furnace bottom and walls have been adequately pheheated, the preheating means are.

withdrawn and the raw materials, indicated above, comprising the initial charge of ingredients for a heat of high chromium high manganese iron or steel are charged into the furnace.

- In the production of a heat of high chromium high manganese iron or steel to a desired specification of chromium, manganese and carbon contents (with or without one or more supplementary additions of 'nickel, copper, aluminum, silicon, molybdenum, tungsten, vanadium and the like in specified amounts), the relative amounts of. chromium contributed by the chromium-containing iron or steel scrap, high carbon ferrochrome and chrome ore, and the relative amounts of manganese contributed by the manganese-containing iron or steel scrap, high carbon ferromanganese and manganese ore, all as used in proportions consistent with good furnace operating conditions, are largely determined by the availability of these various ingredients and the is most expensive as high carbon ferrochrome. I

Chromium in all of these forms, however, is much less expensive than chromium as the generally used low carbon ferrochrome. Similarly, manganese is least expensive in the form of manganese ore and progressively more expensive as manganese-containing scrap iron or steel, high carbon ferromanganese and the generally used low carbon ferromanganese.

To achieve clean, sound, high grade metal at a minimum of expense, a maximum of the less expensive chromium-containing and manganesecontaining ingredients as is consistent with good furnace operation conditions (greatly limited by the permissible volume of slag which may be handled) is therefore employed. Now, since the chromium-bearing ingredients are considerably more expensive than the manganese-containing materials, and since the cost differential between chrome ore and high carbon ferrochrome is appreciably greater than that between manganese ore and high carbon ferromanganese a maximum of the inexpensive chrome ore is preferably used in the practice of my invention.

Where the practice indicates that further volumes of slag may be adequately handled, as in the production of the high chromium high manganese irons and steels of the lower ranges of chromium and manganese contents, much of the addition of manganese may be made in the form of the inexpensive manganese ore. Practice has shown, however, that unsatisfactory" furnacing conditions are encountered where the chromium and manganese additions are made by chrome ore and manganese ore respectively, as for example, in the production of the high chromium high manganese irons and steels of a medium range of analyses.

Highly satisfactory results are achieved in the production of high grade, inexpensive metal by employing a maximum of chrome ore for the chromium addition and the readily available high carbon ferromanganese as the source of manganese. In many instances as in the production of the high chromium high manganese irons and steels of, the upper analyses ranges of chromium and manganese, much of the chromium is added in the form of high carbon ferrochrome.

Where desired the additions of chromium and manganese may be largely made in the form of high carbon ferrochrome and high carbon ferromanganese respectively, or as high carbon ferrochrome-manganese, substituting in whole or in part for additions of chrome ore and manganese ore. Under present market conditions, however, the use of great quantities of high carbon ferrochrome and high carbon ferromanganese as sources of chromium and manganese is found to be appreciably more expensive than the use of substantial quantities of the ores of chromium and manganese for making these additions.

Inthe practice of my process for producing high chromium high manganese irons and steels the amount of high chromium high manganese iron and steel scrap employed as a source of chromium and manganese (as contrasted with the high manganese steel scrap-10% manganese, 1% carbon and the balance ironwhich is well known and readily available) is generally determined by the availability of scrap metal in and around the melt shop and various customer plants. As more particularly indicated in the recently granted Patent No. 2,056,162 of William B. Arness, issued October 6, 1936 and entitled Production of rustless iron, the amount of scrap metal available in balanced manufacture in the form of ingot butts, crop ends and the like, is about 20% of the tapped metal. Where this metal is processed into bar stock the available scrap is then about 25% to 30% of the tapped metal. Where the metal is further processed into sheet and strip at various customer plants for example, the scrap available as ingot butts, crop ends, scrap sheet, punchings, clippings and the like amounts to from 40% to 50% of the metal tapped. This figure may even amount to some 60% or 70% where the sheet or strip is fabricated into various ultimate articles of manufacture, such as machine or burner parts, kitchen ware, automobile trim, architectural applications and similar products. l

' While as an economical measure the amount of high chromium high manganese iron or steel scrap employed in the production or a heat of metal is proportional to that rendered available about the melt shop, this amount may be greatly increased where large quantities of this scrap are available at a favorable market price and simi larly, the amount of scrap employed may be greatly lessened, or omitted entirely, where an acute shortage of scrap is encountered or where the market price of scrap becomes excessive.

The highly flexible nature of my process of producing high chromium high manganese irons and steel assures the production of high grade metal at a minimum of expense by using a maximum of inexpensive raw materials, the relative proportions of which are varied as desired to meet fluctuating conditions of availability and market price.

As illustrative of the practice of my invention, in the production of a heat of high chromium high manganese iron to adesired specification of chromium 17.0% to 19%, manganese-8% to 10%, usual silicon, sulphur and phosphorus and the balance iron, 4,000 pounds of low carbon steel scrap, 6,700 pounds of chromium manganese iron scrap (having an average analysis of chromium 17.5%, manganese 10.0%, carbon .12% and the balance substantially iron), 3,000 pounds of chrome ore (48% CrzOa) 800 pounds of high carbon ferrochrome (analyzing 4% to 6% carbon, 70% chromium and the balance iron), 2,500 pounds of ferro-manganese (analyzing 6% to 8% carbon, manganese and the balance iron), and 4,000 pounds of roll scale, are charged onto the bottom of a chromite lined 6-ton three phase Heroult electric arc furnace rated 25 cycles, to volts, 2500 kva. preheated as indicated above.

Alternating current electrical energy is supplied the furnace and the charge of ingredients begins to melt down forming individual pools of ferrous metal containing carbon, chromium and manganese immediately beneath the furnace electrodes. Under the continuing action of the intense heat of the electric furnace arcs the melting charge of ingredients soon forms a single bath of ferrous metal containing considerable quantities of chromium and manganese and appreciable quantities of carbon as indicated above, covered by a fluid overlying blanket of slag strongly oxidizing in character and rich in the oxides of manganese and chromium.

It may be noted at this point that the presence of considerable quantities of manganese oxides in the blanket of slag overlying the bath of metal renders the slag fluid and'permits a smoother furnace operation with a minimum of dipping of-the furnace carbon or graphite electrodes into the slag and metal and with a consequent minimization of the amount of carbon directly contributed to the metal bath. This is a feature of considerable practical importance where the elimination of carbon requires the use of additional materials and the expenditure of much time and effort. i

'The amounts of chromium and manganese present in the bath of metal atthis stage of the process are largely dependent upon the amount of high chromium high manganese iron or steel scrap added to the charge (and the average chromium and manganese contents of this scrap) and the amount of high carbon ferrochrome and high carbon ferromanganese melted down. Likewise, the quantities of chromium oxide and manganese oxide present in the slag overlying the bath of metal are in a great measure dependent upon the amounts of chrome ore and manganese ore present in the initial charge of ingredients.

The quantities of chromium and manganese appearing in the metal bath as the alloying elements, as compared with the amounts of chromium and manganese appearing in the slag as oxides of chromium and manganese, are further dependent upon the oxidizing character of the slag overlying the metal bath and the tendency for this slag to oxidize these elements from the bath under the operating conditions encountered in practice. The excessive loss of chromium and manganese into the slag as oxides of these elements is effectively prevented, as appears more fully hereinafter, by conducting the melting operation at a temperature of superheat and by initially proportioning relative amounts of chromium and manganese going to form the metal bath and the oyerlying slag.

The strongly oxidizingcharacter of the slag blanket overlying the bath of metal throughout the period of melting down of the charge of ingredients is effective in oxidizing the carbon supplied the bath of metal by the low carbon steel scrap, the chromium-containing or manganesecontaining iron or steel scrap and the high carbon ferrochrome and the high carbon ferromanganese. The practical difliculties in oxidizing carbon from the metal are greatly lessened where the chromium content of the bath is at a minimum. Under these conditions of operation, as where the major portion of the chromium'of the metal is supplied by chrome ore, appearing in this stage of the process .in the slag overlying the bath of metal, and where the manganese content is largely supplied by manganese-containing scrap and high carbon ferromanganese' directly appearing in the ferrous metal bath as a desired alloying addition, the tendency for this path of metal to pick up carbon from the electrodes is reduced to a minimum since manganese does not have the thirst for carbon that is characteristic of chromium.

The strongly oxidizing-character of this slag furthermore acts as an effective barrier between the bath of metal and the furnace carbon or operating temperatures, which for convenience I designate as temperatures of superheat, furthermore assures a very active oxidation of carbon from the metal bath and the realization of an extremely low carbon product in a minimum of time and with the consumption of a minimum of power. 5

While no reliable method is known to me for precisely determining the temperatures of metal and slag during the melt-down period, it is estimated that these temperatures are from about 3100 F. to 3250 F., which is some 150 to 300 F. higher than those ordinarily encountered in ordinary electric steel making practices. The use of such extremely high operating temperatures is permitted, as indicated above, by the highly refractory nature of the chromite brick furnace lining employed.

The excessive oxidation of chromium and manganese from the metal bath, which is ordinarily incidental to the oxidation of carbon, is further lessened by the inhibiting effect of the large quantities of chromium and manganese present in the slag as oxides of chromium'and manganese. The tendency toward the oxidation of these alloying elements from the molten metal is greatly lessened by the initially high balance between the molten chromium and manganese oxides in the slag overlying the metal and the oxides of chromium and manganese dissolved in the metal. In this manner certain further savings are realized in material and labor required to recover chromium and manganese from the slag, as more particularly described hereinafter, thereby achieving a highly efficient and economical process.

When the charge of ingredients is completely melted down and samples taken from the bath for purposes of analysis indicate that the carbon content is several points below the maximum value permissible the melt-down period is at an end. At this stage of the process, there are available in the slag great quantities of iron, chromium and manganese in the form of oxides of these inetals, although much of the iron oxide in the slag has been lost during the melt-down oxidation period in removing and/or excluding carbon from the melting metal and in the oxidation of chromium and manganese incidental to the oxidation of carbon, all as more particularly described above.

The large quantities of metal which are found in the slag as oxides at this stage of the process, are recovered in a reducing period, where preferably a non-carbonaceous reducing agent, such as ferrosilicon, chemically in excess of the oxides of iron, chromium and manganese contained in the slag, is charged onto the slag overlying the bath of metal. The precise amount of reducing agent required to effect a high recovery of the metals from the slag is ordinarily determined empirically.

The contamination of the metal bath with the silicon of the reducing agent during this stage of the process is effectively prevented in spite of the 'use of the excessive quantities of silicon,'by conducting the reduction under strongly basic slag analyses) conditions. The desired basic conditions are preferably achieved by burnt lime in an amount of about three to five times the total silicon content of the ferrosilicon employed. Burnt lime, preferably predried to free the lime of substantially all free and combined moisture normally present,

' is conveniently charged onto the slag along with and lime onto the slag, these ingredients are conveniently mixed on the floor of the melt shop. This mixture is then charged onto the slag overlying the bathof metal from time to time as furnace conditions permit. By charging a large proportion of burnt lime along with the reducing agent in this manner the maintenance of strongly basic slag conditions during the reducing stage of the process is assured.

.By carrying out the reduction of the oxides contained in the slag under strongly basic conditions silicon contamination of the metal is precluded. The acid silicates resulting from the reduction of the reducible oxides of'the slag by the silicon reducing agent employed react with the basic lime added to the slag and form a series of calcium silicates, all as more particularly described in the Patent No. 1,932,252 of William B. Arness, granted October 24, 1933, and entitled Process of producing alloys. These calcium silicates are among the most stable components of the slag.

The large quantities of burnt lime charged onto the slag overlying the bath of metal during the reducing period, as more particularly described above, serve'not only to render'the slag strongly basic and prevent silicon contamination of the metal but also serve to give body to the slag (which is highly fluid and watery because of the large percentage of manganese oxide present in the slag) which in a manner not fully understood by me is effective in achieving a highly efficient reduction of the reducible oxide content of the slag. v

The continued heating of the metal and slag during the prolonged reducing period affords an opportunity to melt down further quantities of chrome ore and manganese ore. These materials are preferably charged along with the silicon reducing agent and burnt lime in corresponding feature particularly important in the production of high chromium high manganese irons and steels of the higher chromium and manganese while maintaining a manageable volume of slag within the furnace throughout both the melt down oxidation period and the subsequent reduction period with a minimum submersion of the furnace electrodes in the furnace metalthereby limiting objectionable carbon pickup from the furnace electrodes throughout the complete process. Illustratively, 2,500 pounds of chrome ore and 200 pounds of pyrolusite (MnOz) are charged along with the ferrosilicon and lime.

After all of the reducing agent, burnt lime and chromium and manganese ores have been added and have fused and completed their reactions with the ingredients present in the slag and metal and a substantially complete recovery of the chromium and manganese are completely recovered is then completely drawn off the metal.

A basic finishing slag of burnt lime and fine ferrosilicon is scattered over the exposed surface of the metal bath. (About 500 pounds "of burnt lime and about 75 pounds of the 75% grade ferrosilicon are employed for the example given.) The heating of the bath is continued at the reduced power input necessary to maintain the metal at a desired temperature until the refining of the metal is completed. The necessary dura tion of the refining period is greatly decreased in the production of high chromium high manganese steels because of the presence of a large percentage of manganese in the metal which is or high chromium high manganese iron ingots analyzing apprommately, .07% carbon, 17.2% chromium, 9.8% manganese, 50% silicon with the usual percentages of sulphur and phosphorus and the balance substantially iron. The metal is clean, sound and comparatively free of objectionable oxide inclusions.

Where desired supplementary additions of nickel, copper, aluminum, silicon, molybdenum, tungsten, vanadium, zirconium and the like may be made in accordance with standard practice either in the furnace or in the ladle.

The production of high chromium high manganese irons and steels with a minimum repair and/or replacement of furnace linings and a. minimum furnace shut-down and loss of operating time, is enjoyed by virtue of the chromite lining employed. This lining, as compared to heretofore known and/or used linings, is particularly resistant to destructive attack, at the high temperatures employed, by the oxidizing meltdown slag followed by the reducing slag used in the second stage of the process, all as more particularly pointed out in my Patent No. 1,925,182,

granted Septemberfi, 1933, and entitled Process for the manufacture of rustless iron. The impervious nature of this material limits the absorption of iron and manganese oxides during the melt-down period and the consequent direct attack upon the furnace lining by a reduction of these oxides during the reducing period, a procedure exceedingly destructive to the lining at the slag line. That part of the bottom and side-walls which is eroded by metal andslag goes into the slag from whichthe reducible oxides are effectively recovered, supplying iron and chromium to the bath of metal, thus, in a measure, compensating for the cost of the erosion of the lining.

Thus, it will be seen that there has been provided in this invention an art of producing high chromium high manganese irons and steels and especially the production of high chromium high manganese irons (metal in which the carbon content ranges as indicated above, from about .05% to .l5%) in which the various objects hereinbefore noted, togetherwith many thoroughly practical advantages are successfully achieved. It will be seen that the process lends itself to the rapid, efiicient and economical production of high chromium high manganese irons and steels employing a maximum of available and inexpensive raw materials consistent with the realization of good furnace operating conditions and the production of clean metal. Because of the presence of a high percentage of maganese in the metal, A and the tendency for manganese to reduce chromium oxides, larger quantities of the inexpensive source of. chromium, chrome ore, are effectively used without risking the production of dirty metal, objectionably contaminated with oxides.

It will be further seen that the process is particularly favorable to obtaining a desired economic balance between the raw materials employed as sources of the alloy metals, chromium and manganese, by relatively adjusting the proportions of ingredients (to such an extent as is consistent with the maintenance of good furnace operating conditions) chromium, manganese iron or steel scrap, chromepre and high carbon ferromanganese, in accordance with variationsln the availability of these materials and the fluctuations in their market prices. I

While as, illustrative of the practice of my invention substantial quantities of chrome ore and 1 manganese ore are added both along with the initial charge of ingredients melted down and with the reducing agent added after melt-down is complete, in order to take advantage of the comparatively long melt-down and reduction periods to effect a thorough heating of these refractory ingredients, it will be understood that chrome ore and/or manganese ore may be added while the melt-down period is in progress, especially toward the end of this period when samples of metal have been taken and the heat of metal is being held in the furnace awaiting a report of herein is to be interpreted as illustrative and not in a limiting sense.

I claim:

In the production of high manganese rustless irons and steels in an electric arc furnace, the art which includes, melting down in said furnace iron scrap, high carbon ferromanganese, high carbon ferrochrome and an oxidizing agent, thereby forming a With of ferrous metal containing chromium and manganese covered by an oxidizing slag containing oxides of manganese and chromium transferred to the slag during the melting down of said ingredients, and after meltdown is complete reducing the oxides contained in said slag, thereby efiecting an enrichment of the bath in manganese and chromium.

' the carbon analysis, in order to realize the benefits of the available furnace heat during this 

